FIG. 1 shows the schematic arrangement of a magnetic disc drive 10 using a rotary actuator. A disc or medium 11 is mounted on a spindle 12 and rotated at a predetermined speed. The rotary actuator comprises an arm 15 to which is coupled a suspension 14. A magnetic head 13 is mounted at the distal end of the suspension 14. The magnetic head 13 is brought into contact with the recording/reproduction surface of the disc 11. The rotary actuator could have several suspensions and multiple magnetic heads to allow for simultaneous recording and reproduction on and from both surfaces of each medium.
An electromagnetic converting portion (not shown) for recording/reproducing information is mounted on the magnetic head 13. The arm 15 has a bobbin portion for holding a driving coil (not shown). A voice coil motor 19 as a kind of linear motor is provided to the other end of the arm 15. The voice motor 19 has the driving coil wound on the bobbin portion of the arm 15 and a magnetic circuit (not shown). The magnetic circuit comprises a permanent magnet and a counter yoke. The magnetic circuit opposes the driving coil to sandwich it. The arm 15 is swingably supported by ball bearings (not shown) provided at the upper and lower portions of a pivot portion 17. The ball bearings provided around the pivot portion 17 are held by a carriage portion (not shown).
A magnetic head support mechanism is controlled by a positioning servo driving system. The positioning servo driving system comprises a feedback control circuit having a head position detection sensor (not shown), a power supply (not shown), and a controller (not shown). When a signal is supplied from the controller to the respective power supplies based on the detection result of the position of the magnetic head 13, the driving coil of the voice coil motor 19 and the piezoelectric element (not shown) of the head portion are driven.
When a magnetic filed is applied to a magnetic material, the domains most nearly parallel to the direction of the applied field grow in size at the expense of the others. This is called boundary displacement of the domains or the domain growth. A further increase in magnetic field causes more domains to rotate and align parallel to the applied field. When the material reaches the point of saturation magnetization, no further domain growth would take place on increasing the strength of the magnetic field.
The ease of magnetization or demagnetization of a magnetic material depends on the crystal structure, grain orientation, the state of strain, and the direction and strength of the magnetic field. The magnetization is most easily obtained along the easy axis of magnetization but most difficult along the hard axis of magnetization. A magnetic material is said to possess a magnetic anisotropy when easy and hard axes exist. On the other hand, a magnetic material is said to be isotropic when there are no easy or hard axes.
In a perpendicular recording media, magnetization is formed easily in a direction perpendicular to the surface of a magnetic medium, typically a magnetic layer on a suitable substrate, resulting from perpendicular anisotropy in the magnetic layer. On the other hand, in a longitudinal recording media, magnetization is formed in a direction in a plane parallel to the surface of the magnetic layer, resulting from longitudinal anisotropy in the magnetic layer.
The requirement for increasingly high areal recording density imposes increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-noise ratio (SNR), and narrow track recording performance. Efforts to produce a magnetic recording medium satisfying such demanding requirements confront significant challenges.
The linear recording density can be increased by increasing the coercivity of the magnetic recording medium. However, this objective can only be accomplished by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise is a dominant factor restricting increased recording density of high density magnetic hard disc drives. Medium noise in thin films is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
It is recognized that the magnetic properties, such as Hr, Mr, S* and SNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by the underlying layers, such as the underlayer. It is recognized that underlayers having a fine grain structure are highly desirable, particular for epitaxially growing fine grains of hexagonal close packed (HCP) Co alloys deposited thereon.
As the demand for high areal recording density increases, the requirements for high recording signal, low media noise and narrow transitions become increasingly difficult to simultaneously satisfy, thereby imposing great demands on film structure design and fabrication techniques. Efforts have been made to explore new types of magnetic and underlayer materials, design new multi-layer thin film structures and manipulate various thin film deposition parameters in attempting to improve magnetic properties and information read/write processes. However, there remains a need for increasingly high areal recording density magnetic recording media exhibiting Hr, high SNR, and narrow signal pulse.
One of the purposes of underlayers has been to nucleate the magnetic film that is subsequently deposited by establishing a match of lattice constant to enhance coercive force and squareness. However, to further extend the increase of areal recording density, a proper choice of underlayers to both reduce grain size and better control crystallographic orientation is desired.